1. Field of the Invention
The present disclosure relates to cold spray systems, and more particularly to powder feeders for cold spray systems with in-situ power blending.
2. Description of Related Art
Cold spray material deposition processes are used to produce dense, pure, thick and well bonded coatings of metals and alloys on target substrates. These coatings typically include metals like aluminum, copper, and nickel, and can also include alloys such as Inconel®. The coatings can be used to form protective or performance enhancing layers, or ultra-thick coatings, on freeform or near net shape substrates. The coatings can also be used to form temperature protection coatings and bond coats for thermal barriers as well as to form protective layers for parts subject oxidation, wear, and/or corrosion. Cold spray is distinguishable from thermal spray in that it typically does not involve melting or near melting the material during the spray process. In contrast, thermal spray involves melting or partially melting the spray material prior to accelerating it the target substrate.
Cold spray processes function by accelerating relatively small particles in a solid state, e.g. a powder, to high velocities in the direction of a substrate target. The accelerated particles impact the substrate to form a continuous layer over the substrate surface. Impact of the accelerated particles disrupts the oxide films on the particles and substrate, pressing their respective atomic structures into intimate contact with one another under high interfacial pressures and temperatures, thereby developing an integral substrate/coating structure. Particles are can be accelerated using a preheated gas, the gas temperature usually lower than the melting temperature of the coating material, generally under 800° Celsius. In some cold spray processes, the gas temperature can be as low as room temperature.
Generally, in order for a cold spray system to develop an acceptable coating, material fed through the system need to be dry, thoroughly blended, and free flowing. This can be particularly challenging for powders comprised of homogenous materials with different sized particles. It can also be problematic for heterogeneous powder mixtures, i.e. mixtures including different constituent material—particularly where the different materials have different particle sizes. Such materials have a tendency to settle or stratify within the powder feeder over time. Stratification in turn causes the relative ratio materials feed through the cold spray system to change while developing the coating on the substrate. This can lead to coatings of non-uniform constitution, excessive porosity, and/or insufficient bond strength. While a concern for cold and thermal spray processes generally, stratification can be of particular concern in cold spray systems as blend mix consistency influences coating consistency, and influences bond strength, deposit density and/or co-deposition of distinct phases. For that reason, cold spray feeders typically employ either or both of mechanical vibration or fluidization for purposes of feeding material through the system.
Such conventional cold spray methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for a powder feeder that allows for improved powder feeding. There is a further need for powder feeders that provide in-situ powder blending. There also remains a need in the art for such a powder feeder that is mobile and easy to make and use. The present disclosure provides a solution for these problems.